Identifying On‐Surface Site‐Selective Chemical Conversions by Theory‐Aided NEXAFS Spectroscopy: The Case of Free‐Base Corroles on Ag(111)

Abstract

We demonstrate here that theory-assisted near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy enables the site-sensitive monitoring of on-surface chemical reactions, thus, providing information not accessible by other techniques. As a prototype example, we have used free-base 5,10,15-tris(pentafluorophenyl)corroles (3H-TpFPC) adsorbed on Ag(111) and present a detailed investigation of the angle-dependent NEXAFS of this molecular species as well as of their thermally induced derivatives. For this, we have recorded experimental C and N K-edge NEXAFS spectra and interpret them based on XAS cross-section calculations by using a continuous fraction approach and core-hole including multiprojector PAW pseudopotentials within DFT. We have characterized the as-deposited low temperature (200 K) phase and unraveled the subsequent changes induced by dehydrogenation (at 330 K) and ring-closure reactions (at 430 K). By exemplarily obtaining profound insight into the on-surface chemistry of free-base corrolic species adsorbed on a noble metal this work highlights how angle-dependent XAS combined with accurate theoretical modeling can serve for the investigation of on-surface reactions, whereby even highly similar molecular structures, such as tautomers and isomers, can be distinguished.

Unraveling the Oxidation and Spin State of Mn–Corrole through X-ray Spectroscopy and Quantum Chemical Analysis

“…The C 1s signal (Figure 1a) can be fitted with four components similarly to its free base equivalent. 32,33 The experimentally determined area ratios for the individual components (15:9:3:7) nicely match the theoretical stoichiometric composition (15:11:3:8) of the synthesized species. The N 1s spectrum (Figure 1b) consists of a single peak with a binding energy of 398.9 eV, which is characteristic for metalated corroles, porphyrins, and phthalocyanine complexes.…”

“…Further details of the method and its application onto free base corroles can be found elsewhere. 32,33 2. All-Electron (AE) Calculations.…”

Tetracene Ultrathin Film Growth on Hydrogen-Passivated Silicon

“…To model the 1s core hole, scalar-relativistic multiprojector GIPAW pseudopotentials with a corresponding occupation of the inner shells were generated. This approach yields reliable results , and is computationally very efficient in describing excitonic effects …”

“…Then, the total NEXAFS spectrum of the molecular system was obtained from the superposition of the individual spectra offset by the corresponding core-level shifts, calculated within DFT − for each carbon atom (see, e.g. , refs , , , and for further details). For structures with axial symmetry, the XAS cross section (σ XAS ) for an E -field component, tilted by an angle θ with respect to the surface normal, can be accurately calculated by averaging over two orthogonal azimuthal orientations (for an arbitrary angle φ 0 ): In the present case, the 3-fold symmetry of the substrate is broken by the attached molecules.…”

The Flexible On-Surface Self-Assembly of a Low-Symmetry Mabiq Ligand: An Unconventional Metal-Assisted Phase Transformation on Ag(111)

“…Figure 7 displays the evolution of the absorption intensity as a function of the photon energy when varying the linear X-ray polarization from largely perpendicular (30°tilted) to parallel to the surface. Compared with previous studies on adsorbed porphyrins, 27,70−72 phthalocyanines, 73,74 and corroles, 75 which typically show a number of distinguishable π* resonances in the pre-edge region below the ionization threshold, the signature of the adsorbed H-Mabiq is simpler, consisting of a single sharp resonance, whose asymmetric line shape may comprise more than one (albeit unresolved) component. This resonance, which can mainly be attributed to the N 1s → π 1 * transition of the iminic nitrogen (−N), 72 is located at 398.2 eV in the RT phase and shifts to a slightly higher photon energy (398.4 eV) in the HT phase, without other appreciable changes.…”